With recent popularization of computers, an inkjet printer is widely used for printing letters or drawing an image on paper, film, cloth or the like not only at offices but also at homes.
The inkjet recording method includes a system of ejecting a liquid droplet by applying a pressure from a piezoelectric element, a system of ejecting a liquid droplet by generating a bubble in the ink under heat, a system of using an ultrasonic wave, and a system of ejecting a liquid droplet by suction using an electrostatic force. The inkjet recording ink used therefor includes an aqueous ink, an oily ink and a solid (fusion-type) ink.
Among these inks, an aqueous ink is relatively superior to oily ink or solid (fusion-type) ink in view of possibility of satisfying all of production, handleability, odor, safety and the like and therefore, is predominating as the inkjet recording ink at present.
The coloring material used in such an inkjet recording ink is required to have high solubility in a solvent (ink medium), enable high-density recording, provide good color hue, exhibit excellent fastness to light, heat, air, water and chemicals, ensure good fixing to an image-receiving material and less blurring, give an ink having excellent storability, have high purity and no toxicity, and be available at a low cost. Various dyes and pigments for use in inkjet recording have been already proposed and are actually used, but a coloring material satisfying all of the above-described requirements is not yet found out at present.
For example, conventionally well-known dyes and pigments such as coloring material having a color index (C.I.) number can hardly satisfy all of those various properties required of the inkjet recording ink.
As for the magenta dye capable of improving the image fastness, azo dyes derived from an aromatic amine and a 5-membered heterocyclic amine have been proposed in Patent Document 1. Furthermore, dyes excellent also in view of color hue are disclosed in Patent Documents 2 and 3. In addition, the color hue and fastness to light are more enhanced by the compounds described in Patent Document 4 or the pyrazolylazoaniline dyes described in Patent Document 5.
As for the cyan dye, phthalocyanine dyes excellent in the water solubility or dispersibility and at the same time, improved in the color hue and fastness to light have been proposed in Patent Documents 6 to 10.
Despite these improvements of the magenta dye and cyan dye, it is required that the yellow dye also has image fastness (namely, preservability) comparable to those of the magenta and cyan dyes so as to draw an image free from change of color hue in aging and capable of maintaining an excellent pictorial quality. However, such a desired yellow dye is not known and therefore, when the image is stored and aged in a place having a strongly oxidative atmosphere such as bright room or outdoors or in a high-temperature and high-humidity place, there arises a problem in many cases that the yellow dye is discolored and the color balance is disrupted.
In addition to the problem of satisfying both color hue and fastness, the aqueous yellow ink is also deficient in that the ejection property is readily worsened and the stability in the state of being charged in a printer is not sufficiently high.
Furthermore, the ink using only water as the dissolution or dispersion medium at the preparation of an ink solution exhibits poor penetrability into the recording medium (such as paper) and the image is often not fixed. Also, the liquid properties necessary for the hitting as an ink are not satisfied in many cases. In order to solve these problems, a technique of using a water-miscible high-boiling point organic solvent as an auxiliary solvent is generally employed in this field. However, it has been found that when a high boiling point organic solvent is used in a large amount, the image formed is disadvantageously liable to blur under high-humidity conditions.
In addition, the aqueous ink is readily putrefied and when the ink is aged for a long time, the ejection property is more deteriorated due to putrefaction. Even if an antiseptic is used in order to maintain the physical properties or ejection property of the ink, the effect of the antiseptic is unstable and can be hardly maintained because the fungus gains resistance.
As described above, the yellow ink for inkjet recording is failing in sufficiently satisfying both excellent image preservability against light, heat and high humidity, and excellent ejection stability at the image drawing. Realization of a yellow ink satisfied in both of these requirements is demanded on the market. Additionally, it is necessary to bring about no blurring of the image drawn and no fluctuation in the liquid properties due to putrefaction or other causes.
[List of Patent Documents as Background Art]
The documents described in the Background Art are as follows.
[Patent Document 1]JP-A-55-161856 (the term “JP-A” as usedherein means an “unexamined publishedJapanese patent application”)[Patent Document 2]JP-A-61-36362[Patent Document 3]JP-A-2-212566[Patent Document 4]JP-T-11-504958 (the term “JP-T” as usedherein means a “published Japanese translationof a PCT patent application”)[Patent Document 5]Japanese Patent Application No. 2000-80733[Patent Document 6]JP-A-2003-3086[Patent Document 7]JP-A-2003-3099[Patent Document 8]JP-A-2003-3109[Patent Document 9]JP-A-2003-12952[Patent Document 10]JP-A-2003-12956
An object of the present invention is to solve the problems of the yellow ink and the like for inkjet recording described in the Background Art, more specifically, an object of the present invention is to provide an inkjet recording ink ensuring excellent ejection stability even after aging of the ink and also exhibiting excellent weather resistance.
Another object of the present invention is to provide an inkjet recording ink ensuring less blurring of the image drawn, in addition to excellent ejection stability and excellent weather resistance.
A still another object of the present invention is to provide a yellow ink, a dark yellow ink and a black ink, which can ensure a pictorial quality with excellent color balance when combined with magenta and cyan inks, in addition to excellent ejection stability, excellent weather resistance and no blurring of image.